1. Field of the Art
This invention relates to a vacuum suction pad useful for attracting, fixing, holding or transferring work or the like by suction force, and a method for manufacturing such suction pads.
2. Description of the Prior Art
Vacuum suction pads, formed of synthetic rubber or flexible synthetic resin material, have been resorted to, for example, in sucking and transferring work such as glass sheets, silicon wafers, liquid crystal material, cathode ray tubes and the like. However, in many cases a suction pad of this sort tends to leave a pad mark on a work surface which has been in contact with the pad.
Such pad marks are mainly attributable to exudation of oily contaminant substances from the pad material, and have possibilities of not only impairing the surface condition of work but also giving adverse effects as contaminants to the atmosphere of a clean room or other spaces where pieces of work undergo a manufacturing process. Besides, such contaminants are likely to cause troubles in a later stage, for example, troubles in the stage of a surface treatment, troubles in the stage of deposition of fluorescent material on cathode ray tubes, or troubles in the stage of bonding liquid crystal with other thin sheet material. Further, the contaminants might be chemically bonded to the material of work in some cases.
Especially in case of vacuum suction pads, even if they are free of exudation under normal conditions, they have possibilities of leaving pad marks after they are internally evacuated to suck a piece of work thereto or when they contain a component which has possibilities of exudation under certain condisions, for example, in depressurized conditions.
There have been made various attempts to overcome the problem of pad marks by improving the composition of the pad material through reductions of the contents of contaminant components. However, so far these attempts have barely succeeded in achieving satisfactory results, in consideration of the influences on the physical properties and workability of the pad material. Therefore, some products require to include a step of wiping off pad marks of the suction pads in a succeeding stage, resulting in an increased number of steps of the manufacturing process. Attempts have also been made to prevent the deposition of pad marks, for example, by the use of a vacuum suction pad which has thin cloth-like fibrous material wrapped or bonded on its sucking surface or inner surface to prevent its direct contact with a work. This measure may succeed in preventing deposition of pad marks but lends itself to degradations in sucking capability of the pad.
Besides, the suction pads are repeatedly subjected to deformations and localized loads to undergo considerable fatigue as they are pressed against work, so that, in addition to the above-mentioned problem of pad marks, it is important to lessen their fatigue and wear by minimizing their frictional resistance on work surfaces to be sucked.